The mitral valve (also called the bicuspid valve) separates the upper left heart chamber from the lower left heart chamber, and helps control blood flow through the heart.
During each heartbeat, the smaller upper chambers of the heart (atria) contract to push blood into the larger lower chambers (ventricles).
The mitral valve opens to allow this passage of blood from the left atrium, and closes when the left ventricle is full of blood, to prevent backflow.
When the valve closes, its two leaflets (flaps) normally seal the valve shut. Tendons attached to these flaps keep them taut and prevent them collapsing through to the other side.
Problems affecting the mitral valve
Problems with the mitral valve can make the heart less efficient at pumping blood around the body. Severe problems can lead to heart failure (where the heart can no longer pump enough blood around the body) if the valve is not surgically repaired or replaced.
Common mitral valve problems are:
- mitral regurgitation (also called 'mitral incompetence') – where there is a backflow of blood through the valve, often as a result of a problem called mitral valve prolapse(where the valve collapses)
- mitral stenosis – where the valve doesn't open as wide as it should, restricting blood flow
These conditions can occur alone or in combination. They are covered in more detail below.
Mitral regurgitation means there is a backflow of blood from the left ventricle to the left atrium when the heart contracts during a heartbeat.
This can cause symptoms such as shortness of breath, tiredness,dizziness and chest pain, and it can lead to atrial fibrillation (a condition that causes an irregular and often abnormally fast heart rate),pulmonary hypertension (high pressure inside the vessels carrying blood from the heart to the lungs) and heart failure.
Mitral regurgitation can happen when the mitral valve flaps fail to seal shut, either because of problems with the flaps (such as a mitral valve prolapse – see below) or due to widening of the mitral annulus, which is the ring of muscle surrounding the valve.
These problems are more common in older people and are often the result of changes to the heart with age. For example, the mitral valve may become weaker due to 'wear and tear' or damage caused by persistent high blood pressure.
Occasionally, mitral regurgitation can occur as a result of rheumatic heart disease (a complication of rheumatic fever), cardiomyopathy (a disease of the heart muscle), endocarditis (infection of the inner lining of the heart), or congenital heart disease (birth defects affecting the normal workings of the heart).
If regurgitation is only mild, you may just be monitored at regular intervals with echocardiography (an ultrasound scan of the heart) to check your heart function.
If you have moderate or severe mitral regurgitation, you'll probably need surgery to repair or replace the valve (see below). You may also need medications called nitrates or diuretics to reduce symptoms such as shortness of breath, and medication to treat atrial fibrillation.
If you have severe mitral regurgitation and you are not suitable for surgery, or you are still having problems after surgery, you may be offered medications called angiotensin-converting enzyme (ACE) inhibitors or beta-blockers to help manage the condition.
Mitral valve prolapse
Mitral valve prolapse means that one or more of the mitral flaps are floppy and don't close tightly, often leading to backflow of blood (mitral regurgitation – see above).
Most people with a mitral valve prolapse will not have symptoms, unless the problem causes severe mitral regurgitation, and it is usually discovered by chance during echocardiography (an ultrasound scan of the heart) carried out for a different reason.
Occasionally, however, mitral valve prolapse can cause problems such as arrhythmia (an irregular heartbeat) and palpitations (sudden, noticeable heartbeats).
Mitral valve prolapse can be caused by problems with the connective tissues (chords) that join the mitral valve to the heart muscles or, more rarely, by damage to the heart muscles themselves as the result of a heart attack. Some people with the condition are born with it and it's more common in people with connective tissue disorders, such asMarfan syndrome.
If mitral valve prolapse isn't causing any symptoms and you are at low risk of developing severe mitral regurgitation, you won't need surgical treatment.
Mild symptoms can sometimes be controlled with lifestyle changes, such as giving up cigarettes, caffeine and alcohol, because these can cause your heart to become overstimulated.
Surgical repair or replacement of the valve (see below) may be recommended if you have:
- severe mitral regurgitation causing symptoms
- no symptoms but an enlarged lower heart chamber
- severe mitral regurgitation with atrial fibrillation or pulmonary hypertension
Mitral valve stenosis
Mitral valve stenosis occurs when the mitral valve doesn't open as wide as it should, restricting the flow of blood through the heart.
As a result, less blood can get to the body and the upper heart chamber swells as pressure builds up. Blood and fluid can also collect in the lungs, making it hard for you to breathe.
The most common cause of mitral valve stenosis in adults is rheumatic fever, which can occur five to 10 years before the heart valve problems began. Rheumatic fever causes the valve to become inflamed (swollen), and over time the flaps of the inflamed valve stick together and become scarred, rigid and thickened.
Rarer causes of mitral valve stenosis include calcium deposits forming around the valve, radiation treatment to the chest and some medications.
Mitral valve stenosis may not cause any symptoms, but common warning signs include shortness of breath and an abnormally fast heart rhythm (atrial fibrillation).
If you don't have any symptoms, your heart function may just be monitored at regular intervals with echocardiography (an ultrasound scan of the heart).
Some people will be offered medications called nitrates or diuretics to reduce the build-up of fluid in the lungs, medication to treat atrial fibrillation and medication to prevent blood clots.
If you have symptoms, you're at risk of heart failure if you do not have an operation either to open up the valve (percutaneous balloon valvuloplasty) or have it replaced. See below for these procedures.
Left untreated, moderate to severe mitral stenosis can lead to heart failure.
Surgery for mitral valve problems
If you have a severe case of mitral regurgitation, mitral valve prolapse or mitral valve stenosis, you will usually need to have a heart valve operation.
Most heart valve operations are performed under general anaesthetic(where you are asleep). They usually involve making a cut down the middle of the breastbone, although some surgeons are increasingly carrying out these operations using small incisions between the ribs (a 'minimal access' approach).
Sometimes it's possible to perform the surgery using a 'percutaneous' method, which involves feeding a catheter (thin, flexible tube) into a large vein in your neck or groin and guiding this through to your heart. People tend to recover more quickly from this procedure, but the results are often less predictable.
The most common mitral valve procedures are:
- mitral valve repair surgery
- mitral valve replacement surgery
- percutaneous balloon valvuloplasty
These procedures are briefly explained below, but your surgeon or heart specialist will explain any operation in detail to you, including the risks and benefits.
It is also possible to carry out procedures similar to mitral valve repair using percutaneous techniques, but these are not covered in any detail here because they not widely used and there are still some uncertainties about them. For more information, you can read:
- NICE guidelines on percutaneous mitral valve repair for mitral regurgitation
- NICE guidelines on percutaneous mitral valve annuloplasty
Mitral valve repair surgery
Repairing the mitral valve flaps is the main surgical treatment for mitral regurgitation.
The operation is carried out under general anaesthetic and your surgeon will usually gain access to your heart through an incision made along your chest. Some surgeons may also perform this type of operation using laparoscopic (‘keyhole’) techniques, and the advantages of this approach are still being evaluated.
The two flaps of the mitral valve are then partially clipped or sewn together to reduce the amount of blood leaking backwards by keeping the flaps close together during each heart contraction.
This operation is generally successful, with only a small chance of major complications.
Mitral valve replacement surgery
Mitral valve replacement is usually only considered if you're unable to have the valve repaired. You will need it if your valve is furred up with calcium deposits or if the leaflets of your valve do not move.
During surgery, your mitral valve is replaced with either a mechanical or bioprosthetic valve, which is made from animal tissue.
This is major open heart surgery performed under general anaestheticand usually involves making an incision along your chest. You'll be put on a heart-lung bypass machine during the operation, which takes over the function of your heart and lungs while the procedure is carried out.
You will usually need to take medication to prevent blood clots for a long period after this operation.
This operation is generally successful, with a small chance of major complications, although the risk of serious and life-threatening problems is generally higher than with mitral valve repair surgery.
Percutaneous balloon valvuloplasty
Balloon valvuloplasty, also known as percutaneous mitral commissurotomy, is a non-surgical treatment option for mitral valve stenosis. It's usually performed by a cardiologist (heart specialist) using just a local anaesthetic (where you remain awake but your skin is numbed).
A catheter is inserted through your skin via a large vein in your groin or neck and passed through to your heart. The tip of the catheter, which has a balloon attached, is positioned directly inside the narrowed valve. The balloon is inflated and deflated several times to widen the valve opening, before the balloon is deflated and removed.
This procedure is most commonly used in young patients who do not have too much calcium deposited on their valve, pregnant women, and patients who are at an increased risk of developing complications from a mitral valve replacement (see above).
Using this method is generally less predictable and less reliable than accessing the valve directly, although recovery is generally faster.
If your GP has suggested you may need surgery, this guide is for you